BEIJING (AP) — Chinese authorities have further tightened controls of social media in the country, warning that people who post comments deemed libelous and that are retweeted 500 or more times will face defamation charges and up to three years in prison.

The official Xinhua News Agency cited judicial authorities as saying that the new rules would also apply to people whose posts are viewed by at least 5,000 Internet users.

The decision issued Monday comes as authorities have waged a campaign to clamp down on what they’ve termed “online rumors,” but which critics say amounts to a curbing of free speech. State media have also accused some microbloggers of undermining socialism and promoting Western values through lies and negative news.

Many famous Chinese — from pop stars to scholars, journalists to business tycoons — have amassed substantial online followings and some call attention to social injustices and question government policies.

In August, popular microbloggers were asked at a meeting in Beijing to agree to seven standards: obey the law, uphold the socialist system, guard the national interest, protect individual rights, keep social order, respect morals and ensure factuality.

The new rules issued by China’s Supreme People’s Court and Supreme People’s Procuratorate provide some clarity on how authorities will prosecute Internet speech-related activities deemed illegal.

The rules define “serious cases” of such libelous postings by the social and financial damage caused, Xinhua said.

Xinhua said in a commentary that the rules targeted those who sought to defame and blackmail others online.

“These cases have done greater social harm than traditional offenses, with some even disrupting social order and triggering unrest,” the agency wrote.